[NaCl SDK] Bump version of visual studio addin that we ship 1568 -> 1573

This fixes a couple of issues with the installer script regarding
installing on machines that don't have both 2010 and 2012 installed.

R=binji@chromium.org

Review URL: https://codereview.chromium.org/290013003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@271472 0039d316-1c4b-4281-b951-d872f2087c98

native_client_sdk/src/build_tools/json/naclsdk_manifest2.json

@@ -29,7 +29,7 @@
       "name": "vs_addin",
       "recommended": "no",
       "repath": "vs_addin",
-      "revision": 1568,
+      "revision": 1573,
       "stability": "dev",
       "version": 0
     },